Elasticity Of Outer Boundary And The Similar Structure Of Pressure Distribution In The Oil And Gas Reservoir

In view of the fact that the previous seepage model always assumes that the outer boundary conditions are idealized situation of infinite,constant pressure and closed.It is bound to cause a difficult situation to describe the reservoir well,which brings unavoidable error in analysis.In order to solve this practical problem,this paper introduces the concept of elastic outer boundary conditions for the first time,and regards the previous three outer boundary conditions as its special case.Secondly,it also aims at the plane radial flow of homogeneous reservoir.And under the elastic outer boundary condition,a model of seepage considering the wellbore storage and skin factor and a model of seepage considering the wellbore storage and introducing effective well radius are established respectively.Thirdly,by the Laplace transform,and combining with a method which is Similarity Construction Method for solving the boundary value problem for a class of v order variant Bessel equations.The seepage model in Laplace space under the elastic outer boundary condition has similar structure solution.Finally,the dimensionless bottom hole pressure is inverted real space by using Stehfest numerical inversion method,and the characteristic curves are drawn and the impacts of the variation of the related parameters on the curves are analyzed.The results show that the three traditional outer boundary conditions(infinite,constant pressure and closed)are actually three special cases of the elastic outer boundary condition.The dimensionless bottom hole pressure curve under the elastic outer boundary condition is between the dimensionless bottom hole pressure curve of the closed outer boundary condition and the constant pressure outer boundary condition,and the curves above exhibit affine similarities.In this paper,the elastic outer boundary condition is introduced not only to enlarge the range of data interpretation,but also greatly improves the situation that the reservoir parameters cannot be explained well due to the deviation of the data.The Similarity Construction Method also greatly simplifies the complex solution process of the seepage mathematical model,and it also provides a scientific and simple method for the preparation of well tests analysis software.